(3a-b)²=(3a)²-2*3a*b+b²=9a²-6ab+b²
1.
x=7,13 +-0,04
x min = 7,13-0,04 = 7,09
x max = 7,13+0,04 = 7,17
x∈[7,09; 7,17]
2.
y = (x max + x min) / 2 = (5,782 + 4,138) / 2 = 4,96
a = x max - y = y - x min = 5,782 - 4,96 = 0,822
√3,6*√8,4/√0,21=√[(36*0,84)/0,21]=√(36*4)=6*2=12